CVE-2026-21859 Scanner

Mailpit is widely used as an open-source email testing tool by developers to catch and investigate email content locally without sending it to real users. It typically allows users to view, search, and debug emails generated by their development applications. By providing a safe environment to capture emails, it ensures developers can efficiently test email handling code. Mailpit is frequently utilized in both individual and organizational settings due to its ease of use. The testing environment can be deployed on local machines, enhancing workflow productivity while keeping test data secure in a controlled development context. With the periphery of its functions, Mailpit contributes significantly to streamlining the development-operations process.

Server-Side Request Forgery (SSRF) is a vulnerability that allows an attacker to make requests to arbitrary domains through a vulnerable web server. In the context of Mailpit, it arises from insufficient validation of incoming requests at the /proxy endpoint. This allows attackers to craft HTTP GET requests that the vulnerable server then processes and forwards to any internal network resources. This type of vulnerability can be critical as it may lead to unauthorized access to sensitive data. Through its exploitation, malicious actors can perform reconnaissance and potentially breach other areas of the internal network. SSRFs are notably dangerous because they can exploit trusted connections within the intranet, bypassing typical firewall protections.

The vulnerability in Mailpit is specifically found in its /proxy endpoint, where improper validation of internal IP addresses leads to exposure. The endpoint accepts crafted HTTP GET requests, causing Mailpit to act as a proxy, relaying requests to specified internal URL paths. Attackers exploit this flaw by injecting their own URL parameters into requests, enabling them to interact with services otherwise protected by firewall or network segmentation. Technical analysis highlights that such exploitation can yield access to sensitive information represented in JSON format, with endpoints revealing database versions, statistics, and runtime states. This endpoint, when left unpatched, permits attackers to bypass surface defenses and potentially manipulate data flow.

An SSRF vulnerability being exploited in Mailpit might lead to several critical issues. If attackers gain access to internal network services, they could exfiltrate sensitive information, such as system metadata, configurations, or even internal communications. Also, SSRF could act as a foothold for executing additional attacks, such as further penetration testing or exploiting other vulnerabilities within the network. There is the risk of attackers manipulating internal services to trigger further vulnerabilities, creating a broader security breach than originally apparent. Unchecked, this could ultimately lead to data breaches or unauthorized command executions. Organizations could face substantial reputational damage if sensitive information is leaked as a result.

REFERENCES

• https://rosecurify.com/advisories/RO-26-001-mailpit-server-side-request-forgery-ssrf/
• https://github.com/axllent/mailpit/security/advisories/GHSA-8v65-47jx-7mfr